A variety of microwave devices utilize dielectric material including those with the nominal formulas Ba.sub.2 Ti.sub.9 O.sub.20, BaTi.sub.4 O.sub.9, and ZrTiO.sub.4, with or without other additives, such as tin [e.g., ZrTiO.sub.4 (Sn)]. Typical devices are dielectric resonator filters, microwave stripline circuits, various types of oscillators, as well as phase shifters, bandpass filters, etc. The material requirements for microwave devices include, at least, moderately high dielectric constant, low loss at the appropriate frequency and a high temperature stability.
The widespread use of the dielectric material in microwave devices occurred with the discovery that a material of the nominal formula Ba.sub.2 Ti.sub.9 O.sub.20 has low temperature coefficients of frequency (T.sub.f), high dielectric constants (K) and low microwave losses (high Q). This material is described in a number of references including U.S. Pat. No. 3,938,064 issued to H. M. O'Bryan, Jr., et al. on Feb. 10, 1976, U.S. Pat. No. 4,337,446 issued to H. M. O'Bryan, Jr. et al. on Jun. 29, 1982, and U.S. Pat. No. 4,563,661 issued to H. M. O'Bryan, Jr. et al. on Jan. 7, 1986, each of which is incorporated herein by reference.
These materials are produced by a lengthy and labor and energy demanding processing. Typically the processing involves numerous steps which include formulating a composition, mixing (e.g. ball milling), drying, screening, calcining, comminuting by ball milling, drying, screening (or remilling and spray drying), forming into a suitable shape and sintering. These steps may extend over a period of 72 hours or more prior to the forming step. A flow chart of a representative conventional (prior art) processing is illustrated in FIG. 1 of the drawings.
It is highly desirable to produce these materials by a less cumbersome process and, yet, to obtain a material useful for microwave devices.